1. Field of the Invention
The present invention relates to a transmission/reception unit suitable for use in a portable telephone, etc.
2. Description of Related Art
Referring to FIGS. 10 and 11, a conventional transmission/reception unit has a wiring pattern 52 and ground patterns 53a and 53b on a circuit board 51 constituting a printed circuit board, etc, where an antenna 54 as a conductor is formed on this circuit board 51.
The antenna 54 comprises a linear belt antenna element 55, and transmission and reception terminals 56 and 57 and a ground terminal 58 which are located on one end of the antenna element 55.
Various electric components (not shown) which make up transmission and reception circuitry are connected to the wiring pattern 52 on the circuit board 51, and the transmission and reception terminals 56 and 57 of the antenna 54 are connected through the wiring pattern 52 to the transmission and reception circuitry and the ground terminal 58 is grounded via the ground pattern 53a. 
The ground patterns 53a and 53b are connected via a ground pattern (not shown) formed virtually on the whole lower surface of the circuit board 51, though not shown in these figures.
A hexahedral box type cover 59 is made of sheet metal. It has a square top wall 60, a first side wall 61, a second side wall 62, a third side wall 63 and a fourth side wall 64, a notch 61a made at the bottom of the first side wall 61, and four corners 65a, 65b, 65c and 65d (first, second, third and fourth corners, respectively), where the side walls are formed by bending down the four sides of the top wall 60, and the corners are defined by the side walls.
The cover 59 rests on the circuit board 51 in a way that it covers the electric components disposed on the circuit board 51 except the antenna 54, and the first, second, third and fourth side walls (61, 62, 63, 64) are fixed to the circuit board 51 by soldering their bottoms to the ground pattern 53b. 
The position of the cover 59 on the circuit board 51 is determined by mounting legs (not shown) provided at the bottom of the first and third side walls 61 and 63 which are inserted into holes (not shown) in the circuit board 51. With the cover 59 in place, the antenna element 55 of the antenna 54 lies along the first side wall 61.
Also, with the cover 59 in place, the transmission and reception terminals 56 and 57 and the ground terminal 58 are located in the vicinity of the first corner 65a, and there is a notch 61a above the wiring pattern 52 connected with the transmission and reception terminals 56 and 57 of the antenna 54 and the ground pattern 53a so that the wiring pattern 52 and the ground pattern 53a are electrically isolated from the first side wall 61.
The ground pattern 53a connected with the ground terminal 58 of the antenna 54 is connected to the ground pattern 53b through the ground pattern provided on the rear face of the circuit board 51. The conventional transmission/reception unit is structured as mentioned above.
FIG. 11 illustrates the electrical length of the ground conductor connected with the ground terminal 58 of the antenna 54 in the conventional transmission/reception unit. As shown in the figure, the electrical length L of the ground conductor in the conventional unit is the sum of the following lengths: a length L31 of the ground pattern 53a between the ground terminal 58 and the ground pattern on the rear face of the circuit board 51; a length L32 of the ground pattern on the rear face of the circuit board 51 which lies in the area corresponding to the area between the ground pattern 53a and the first corner 65a of the cover 59; a length L33 as the distance from the bottom of the first or second side wall to its top; and a length L34 as the distance from the first corner 65a to the fourth corner 65d on the top wall 60.
Namely, the electrical length L of the conventional ground conductor is expressed by L31+L32+L33+L34. It is desirable that this electrical length L be equal to the length xcex/4 of the antenna element 55 of the antenna 54. However, as demand for a more compact transmission/reception unit is growing, there is a tendency to reduce the size of the cover 59, resulting in a decrease in the lengths L31, L32, L33 and L34. As a consequence, the electrical length L tends to be shorter than the length xcex/4.
Regarding the length xcex/4 of the antenna element 55, as the frequency becomes lower, the wavelength becomes longer (i.e. xcex/4 increases); however, in the conventional unit, a sufficient electrical length L could not be obtained at high frequencies and low frequencies.
When the antenna 54 is formed on the circuit board 51, if it has a linear antenna element 55 having the required length, the circuit board 51 must be large enough to accommodate it, so the circuit board 51 cannot be compact enough. In addition, the circuit board 51 is on the reverse of the side on which the antenna element 55 is exposed, resulting in a larger loss in radio wave radiation and radio wave reception at the antenna element 55.
Therefore, the problem of the conventional transmission/reception unit is summarized as follows: the electrical length L of the ground conductor connected with the ground terminal 58 of the antenna 54 (L31+L32+L33+L34) is shorter than xcex/4; as the cover 59 becomes smaller, the electrical length L becomes shorter, namely its difference from the length xcex/4 becomes larger, which leads to a decrease in the gain of the antenna 54 and thus a decrease in its transmission/reception sensitivity.
In view of the above circumstances, an object of the present invention is to provide a transmission/reception unit in which an electrical length of the ground conductor connected with the ground terminal of the antenna is sufficiently long and the antenna gain is improved.
As a first solution to the above problem, the invention provides a transmission/reception unit comprising:
a circuit board having a wiring pattern including various electric components;
a cubic or hexahedral box type cover made of sheet metal which is mounted in such a manner as to cover the electric components; and
an antenna mounted on the circuit board, the cover having:
a top wall;
a first, a second, a third and a fourth side walls which are formed by bending four sides of the top wall;
a first corner defined by the neighboring first and second side walls;
a second corner defined by the first side wall and the neighboring third side wall;
a third corner defined by the second side wall and the neighboring fourth side wall; and
a fourth corner defined by the neighboring third and fourth side walls,
the antenna having:
an antenna element as a conductor laid along the first side wall of the cover; and
transmission and reception terminals and a ground terminal which are provided in the vicinity of the first corner and located at one end of the antenna element, wherein the ground terminal is connected to a ground pattern provided on the circuit board, the first corner of the cover or its vicinity is soldered to the non-ground wiring pattern, and the ground pattern is connected with the second corner or its vicinity, or the third corner or its vicinity, or the fourth corner (located diagonally to the first corner) or its vicinity, or part of the third or fourth side wall.
As a second solution, the fourth corner or its vicinity is connected to the ground pattern, and an electrical length of the ground conductor connected to the ground terminal of the antenna consists of: a length of the ground pattern extending from the ground terminal to the fourth corner or its vicinity; a length as a distance from a point of connection with the ground pattern to a top of the third or fourth side wall; a length as a distance on the top wall between the first corner and the fourth corner; and a length as a distance from a top of the first or second side wall to its bottom.
As a third solution, the third corner or its vicinity is connected to the ground pattern, and an electrical length of the ground conductor connected to the ground terminal of the antenna consists of: a length of the ground pattern extending from the ground terminal to the third corner or its vicinity; a length as a distance from a point of connection with the ground pattern to a top of the second or fourth side wall; a length as a distance on the top wall between the second corner and the third corner; and a length as a distance from a top of the first or third side to its bottom.
As a fourth solution, the second corner or its vicinity is connected to the ground pattern, and an electrical length of the ground conductor connected to the ground terminal of the antenna consists of: a length of the ground pattern extending from the ground terminal to the second corner or its vicinity; a length as a distance from a point of connection with the ground pattern to a top of the first or third side wall; a length as a distance on the top wall between the second corner and the third corner; and a length as a distance from a top of the second or fourth side wall to its bottom.
As a fifth solution, part of the third side wall located between the second and fourth corners is connected to the ground pattern, and an electrical length of the ground conductor connected to the ground terminal of the antenna consists of: a length of the ground pattern extending from the ground terminal to part of the third side wall; a length as a distance from a point of connection with the ground pattern to a top of the third side wall; a length as a distance on the top wall from this point on a top to the first or third corner; and a length as a distance from a top of the first, second or fourth side wall to its bottom.
As a sixth solution, part of the fourth side wall located between the third and fourth corners is connected to the ground pattern, and an electrical length of the ground conductor connected to the ground terminal of the antenna consists of: a length of the ground pattern extending from the ground terminal to part of the fourth side wall; a length as a distance from a point of connection with the ground pattern to a top of the fourth side wall; a length as a distance on the top wall from this point on a top to the first or second corner; and a length as a distance from a top of the first, second or third side wall to its bottom.
As a seventh solution, the antenna consists of a base made of an insulating material, an antenna element wound around the outer face of the base and transmission and reception terminals and a ground terminal which are provided on the outer face of the base, and with the antenna element lying over a notch made along the first side wall on the circuit board, both ends of the base rest on the circuit board while the transmission and reception terminals are connected to the wiring pattern and the ground terminal is connected to the ground pattern.
As an eighth solution, the antenna has conductive connections which are connected with the transmission and reception terminals and the ground terminal, respectively; the connections connected with the transmission and reception terminals are connected to the wiring pattern while the connection connected with the ground terminal is connected to the ground pattern and constitutes part of an electrical length of the ground conductor.
As a ninth solution, the transmission/reception unit, the base is made of ceramic.